1. Field of the Invention
The present invention relates to symbol timing in the receivers of wireless communication systems, and, in particular, in the receivers of multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless local area networks (LANs) and broadband wireless access systems.
2. Description of the Related Art
Combining the spectral efficiency of MIMO with the robustness against frequency-selective fading and narrowband interference of OFDM is regarded as a very promising starting point for future high-data-rate radio communication systems. This is especially true for wireless LANs (WLANs), where MIMO would open the door to high-data-rate extensions by extending current OFDM standards in the 2.4 and 5 GHz bands.
In the recent past, various transmission schemes for MIMO have been proposed, but the impact of system imperfections have generally been neglected. Furthermore, the systems were typically assumed to be perfectly synchronized. Thus, signal impairments caused by the radio system (e.g., frequency offset, phase noise) have not been considered.
Various synchronization techniques for single-input single output (SISO) OFDM systems have been proposed in the literature. See, e.g., T. M. Schmidl and D. C. Cox, Robust Frequency and Timing Synchronization for OFDM, IEEE Transactions on Communications, vol. 45, no. 12, December 1997, pp. 1613-1621, and P. H. Moose, A Technique for Orthogonal Frequency Division Multiplexing Frequency Offset Correction, IEEE Transactions on Communications, vol. 42, no. 10, October 1994, pp. 2908-2914, the teachings of both of which are incorporated herein by reference. Few techniques, however, have been proposed to synchronize MIMO OFDM systems. Data-aided synchronization for MIMO OFDM systems is proposed in one paper, but the performance exploration of the proposed techniques is very concise. See A. N. Mody and G. L. Stüber, Synchronization for MIMO OFDM Systems, IEEE Global Communications Conference 2001, vol. 1, November 2001, pp. 509-513, the teachings of which are incorporated herein by reference.